1. Field of the Invention
The invention relates to an electric vehicle that includes a motor that is able to regenerate electric power from kinetic energy of the vehicle and a control device for the electric vehicle. The electric vehicle in the specification also includes a hybrid vehicle that includes an engine together with such a motor, and a fuel cell vehicle.
2. Description of Related Art
An electric vehicle, different from an existing engine vehicle, includes an electrical system that handles large current. The electrical system includes a motor that is able to regenerate electric power from kinetic energy of the vehicle, a large-capacity large-current battery, an inverter that converts direct-current power of the battery to alternating-current power suitable for driving the motor, and the like. Therefore, various safety measures and preventive measures, which are not equipped for an engine vehicle, are taken. Note that the motor that is able to regenerate electric power from kinetic energy of the vehicle may also serve as a wheel drive motor (that is, a motor that serves as a device that generates driving force).
For example, Japanese Patent Application Publication No. 2007-216833 describes a technique for preventing the following situation. When an engine stop signal is input to a control device while a hybrid vehicle is travelling, the engine is forcibly stopped, so large current flows through a motor, and the amount of discharge of a main battery exceeds an upper limit, causing a decrease in battery service life.
There is one of measures peculiar to an electric vehicle for a situation that a driver erroneously switches a main switch of the vehicle to the OFF position or returns the main switch to the ON position again while travelling. Here, the main switch of the vehicle means a switch provided at a driver seat and is generally called “ignition switch”. In the case of an electric vehicle, when the main switch is at the ON position, a relay that connects the inverter to the main battery is closed (the main battery is connected to an electrical system of the motor), and the motor is being driven or is in a drivable state. When the main switch is at the OFF position, the relay between the inverter and the main battery is open, and supply of electric power to the motor is stopped. In the case of a hybrid vehicle that includes a motor and an engine, when the main switch is at the ON position, a relay that connects the inverter to the main battery is closed (the electrical system of the motor is connected to the main battery), the motor is being driven or is in a drivable state, and the engine is also being driven or in a drivable state. At the OFF position, supply of electric power to the motor is stopped, and supply of fuel to the engine is also stopped. In addition, in the electric vehicle (including a hybrid vehicle), when the main switch of the vehicle is at the OFF position, an overall system associated with a drive system is stopped. Here, the system associated with the drive system typically includes an inverter and a cooling system for the inverter or a motor. Hereinafter, for the sake of simple description, switching the main switch of the vehicle from the ON position to the OFF position is referred to as “ON/OFF switching”, and switching the main switch from the OFF position to the ON position again is referred to as “OFF/ON switching”.
ON/OFF switching of the main switch while travelling is not a normal usage mode; however, the driver may erroneously conduct such an operation. When the main switch is switched from the ON position to the OFF position, supply of electric power to the motor (and supply of fuel to the engine), the inverter and the cooling system are stopped, but the motor continues rotating by the inertia force of the vehicle. When OFF/ON switching of the main switch is performed again while travelling, the inverter and the cooling system start up in a state where the motor is rotating. As a result, upon OFF/ON switching, a high load may is applied to the inverter and the cooling system. For example, when the inverter starts up while the motor is rotating due to coasting of the vehicle, the function of recovering regenerative electric power is activated, and the inverter operates to convert counter electromotive force, generated by the motor, to direct-current power. A high load is applied to the inverter immediately after OFF/ON switching of the main switch, and the inverter generates heat. In addition, while the main switch is OFF, motor coils form an open system because the main relay that connects the inverter to the battery is open, so no current (counter electromotive force) flows; whereas the motor coils form a closed system when the main relay is closed, so counter electromotive force flows. Then, the motor itself also generates heat. As described above, when OFF/ON switching of the main switch is performed while travelling, the cooling system of the inverter (and/or the motor) has just started up, so a response to steep heat generation of the inverter (and/or the motor) delays.